Crystal structures and phase transition of tetrafluoroethylene-vinyl alcohol alternating copolymer
Crystal structures and phase transition of tetrafluoroethylene-vinyl alcohol alternating copolymer
复制标题
四氟乙烯-乙烯醇交替共聚物的晶体结构和相变
DOI：
10.1016/j.polymer.2021.124354
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发表时间：
2021
期刊：
影响因子：
4.6
通讯作者：
Okura Masahiro
中科院分区：
文献类型：
--
作者：
Tashiro Kohji;Okura Masahiro
通过X射线衍射和红外光谱数据分析，研究了一种新型含氟聚合物或四氟乙烯-乙烯醇(TFE-VA)交替共聚物的晶体结构和热致相变。根据结晶条件的不同，共聚物表现出三种结晶改性。以有机溶液为原料，在室温下浇注，制得晶型改性β。分子链由之字形构象轻微收缩，堆积在正交晶胞中(a=99.48；b=95.38；c(链轴)：x=99.84)，空间群对称性为：P21cn。在170℃以上加热β形式会导致不可逆的向高温α形式(αHT)的转变。这样创建的αΗΤ阶段不能再更改回β表单。熔体的冷却首先诱导晶化为α高温相，在135℃以下明显连续且可逆地转变为低温α相(αLT)。αLT由几乎完全伸展的链在晶胞中的统计无序堆积组成，ofa=99.58；b=95.48；α高温采用与αLT相似的晶体结构，但之字链被包装在略大的单元格ofa=910.01；b=95.64；c(链轴)o=95.02；(在170℃时)处于更高度无序的状态，链的热激活运动。在这些晶相中，形成了F⋯H-O和O⋯H-O类型的氢键，从而稳定了链堆积结构。
Crystal structure and thermally-induced phase transition have been studied for a novel fluorine polymer or tetrafluoroethylene-vinyl alcohol (TFE-VA) alternating copolymer on the basis of the X-ray diffraction and infrared spectroscopic data analyses. The copolymer exhibits the three kinds of crystalline modification depending on the crystallization conditions. The crystal modification β is obtained by casting from the organic solution at room temperature. The molecular chains are slightly contracted from the zigzag conformation and are packed in the orthorhombic unit cell (a= 9.48 Å,b= 5.38 Å andc(chain axis) = 9.84 Å) with the space group symmetry ofP21cn. The heating of the β form above 170 °C causes the irreversible transition to the high-temperature α form (αHT). The thus-created αΗΤphase cannot change back to the β form anymore. The cooling from the melt induces the crystallization to the αHTphase at first, which transforms to the low-temperature α phase (αLT) apparently continuously and reversibly below 135 °C. The αLTform consists of the statistically disordered packing of the almost fully-extended chains in the unit cell ofa= 9.58 Å,b= 5.48 Å andc(chain axis) = 5.01 Å. The αHTtakes the similar crystal structure to that of the αLT, but the zigzag chains are packed in the slightly larger unit cell ofa= 10.01 Å,b= 5.64 Å andc(chain axis) = 5.02 Å (at 170 °C) in more highly disordered state with thermally-activated motion of the chains. In these crystalline phases, the hydrogen bonds of F⋯H-O and O⋯H-O types are formed to stabilize the chain packing structures.
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